Akira Mohri

Bio: Akira Mohri is an academic researcher from Kyushu University. The author has contributed to research in topics: Motion planning & Trajectory. The author has an hindex of 17, co-authored 109 publications receiving 836 citations.

Trajectory planning of mobile manipulator with stability considerations

Abstract: This paper presents methods of trajectory planning for a mobile manipulator with stability considerations. The proposed trajectory planning method is to generate a trajectory for the mobile manipulator from a given path of the end-effector considering stability. Then, we derive a dynamics model of the mobile manipulator considering it as the combined system of the manipulator and the mobile platform. ZMP criterion is used as an index for the system stability. The trajectory planning problem is formulated as an optimal control problem with some constraints. To solve the problem, we use a hierarchical gradient method which synthesizes the gradient function in a hierarchical manner based on the order of priority. The simulation results of the 2-link planar nonholonomic mobile manipulator are given to show the effectiveness of the proposed algorithm.

Inverse dynamics and control of crane-type manipulator

Abstract: This paper discusses an inverse dynamics problem for a parallel wire mechanism with multi-degrees of freedom. Firstly, a crane-type parallel wires mechanism which has three trolleys and three wires is proposed for handling heavy objects. This handling mechanism enables not only three dimensional positioning but also orientating of objects, unlike typical crane mechanism. A dynamical model using wire force vector is derived. Based on the dynamical model with wire force vector, inverse dynamics problem is analytically solved by a linear equation in terms of the wire force vector. The trajectory of end-effector of the crane-type manipulator can be transformed into the trajectory of wire length and trolley position by the calculation method. Using the trajectory of wire length and trolley position, the end-effector of the crane-type manipulator is controlled. Two dimensional experimental crane-type manipulator is also developed to verify an effectiveness of the inverse dynamics calculation and the trajectory control method.

Quasi-time-optimal motion planning of mobile platforms in the presence of obstacles

Abstract: This paper addresses a problem of optimal motion planning of mobile platforms amidst obstacles, considering the mobile platform dynamics. Due to nonholonomic constraints, actuator constraints, and state constraints by obstacle avoidance, the planning problem of mobile platform with two independently driven wheels is a complicated one. In this study, a dynamical model for the mobile platform is presented, including nonholonomic kinematic constraints. The idea of a path parameter is introduced to simplify the planning problem by considering the dynamics and nonholonomic constraints. Using the path parameter, the optimal motion planning problem is divided into two sub-problems: 1) time-optimization of trajectory along specified path, and 2) search for optimal path. Then two methods are proposed the solve the problems using the path parameter and parametrization by B-spline function. Finally, quasi-time-optimal solution for the original problem are planned by combining the two methods. Numerical examples show effectiveness of the motion planner.

Sub-optimal trajectory planning of mobile manipulator

Abstract: A trajectory planning method of a mobile manipulator is presented. We derive the dynamics of the mobile manipulator considering it as the combined system of the manipulator and the mobile platform. The planning problem is formulated as an optimal control problem. To solve the problem, we use the concept of the order of priority. A gradient-based iterative algorithm which synthesize the gradient function in a hierarchical manner based on the order of priority is used. The simulation results of the 2-link planar nonholonomic mobile manipulator are given to show the effectiveness of the proposed algorithm.

Cooperative path planning for two manipulators

Abstract: This paper proposes a method of planning collision free joints paths for two cooperative manipulators. When two manipulators hold a common object and execute specified tasks, there are problems related to handling and collision. To move two manipulators effectively, all of them must be considered together. There are redundancy aspects peculiar to the cooperative two manipulators. We use this redundancy and the potential function method to avoid collisions between the object and the link, the link and the link, the link and the obstacle and so on. Simulation results show the effectiveness of the proposed method.

Model-based recognition and localization from sparse range or tactile data

Abstract: This paper discusses how local measurements of three-dimensional positions and surface normals (recorded by a set of tactile sensors, or by three-dimensional range sensors), may be used to identify and locate objects from among a set of known objects. The objects are modeled as polyhedra having up to six degrees of freedom relative to the sensors. We show that inconsistent hypotheses about pairings between sensed points and object surfaces can be discarded efficiently by using local constraints on distances between faces, angles between face normals, and angles (relative to the surface normals) of vectors between sensed points. We show by simulation and by mathematical bounds that the number of hypotheses consistent with these constraints is small We also show how to recover the position and orientation of the object from the sensory data. The algorithm's performance on data obtained from a triangulation range sensor is illustrated.

A survey of robot tactile sensing technology

Abstract: This paper reviews the current state-of-the-art in tactile sens ing technology. We examine in detail the different methods of transduction employed by tactile sensors and describe various significant designs that incorporate these methods. We then describe the different techniques used to process and analyze tactile data. Finally, we conclude with an assessment of the current state of development.

Elastic Strips: A Framework for Motion Generation in Human Environments

Abstract: Robotic applications are expanding into dynamic, unstructured, and populated environments. Mechanisms specifically designed to address the challenges arising in these environments, such as humanoid robots, exhibit high kinematic complexity. This creates the need for new algorithmic approaches to motion generation, capable of performing task execution and real-time obstacle avoidance in high-dimensional configuration spaces. The elastic strip framework presented in this paper enables the execution of a previously planned motion in a dynamic environment for robots with many degrees of freedom. To modify a motion in reaction to changes in the environment, real-time obstacle avoidance is combined with desired posture behavior. The modification of a motion can be performed in a task-consistent manner, leaving task execution unaffected by obstacle avoidance and posture behavior. The elastic strip framework also encompasses methods to suspend task behavior when its execution becomes inconsistent with other const...

Control of flexible manipulators: A survey

Abstract: A survey of the field of control for flexible multi-link robots is presented. This research area has drawn great attention during the last two decades, and seems to be somewhat less “attractive” now, due to the many satisfactory results already obtained, but also because of the complex nature of the remaining open problems. Thus it seems that the time has come to try to deliver a sort of “state of the art” on this subject, although an exhaustive one is out of scope here, because of the great amount of publications. Instead, we survey the most salient progresses – in our opinion – approximately during the last decade, that are representative of the essential different ideas in the field. We proceed along with the exposition of material coming from about 119 included references. We do not pretend to deeply present each of the methods quoted hereafter; however, our goal is to briefly introduce most of the existing methods and to refer the interested reader to more detailed presentations for each scheme. To begin with, a now well-established classification of the flexible arms control goals is given. It is followed by a presentation of different control strategies, indicating in each case whether the approach deals with the one-link case, which can be successfully treated via linear models, or with the multi-link case which necessitates nonlinear, more complex, models. Some possible issues for future research are given in conclusion.